Electronic tube and circuits



Dec. 9, 1952 w. H. CHERRY ELECTRONIC TUBE AND CIRCUITS Filed Mach 51. 1949 Fic-9:1.

Cttorn g Patented Dec. 9, 1 952 UNITED STATES ELECTRONIC TUBE yAND CIRCUITS William Henry Cherry, Princeton, N. J., assignol to Radio Corporation of America., a corporation of Delaware Application March 31, 1949, Serial No. 84,538

( Cl.v 315-27) 3 Claims.

My invention relates to an improvement in amplifiers and to an improved circuit forv use with cathode ray tubes.

Considerable diiculty has been experienced in coupling the output of standard sweep generators to the beam deecting elements of a cathode ray tube because spurious oscillations are set up in the output amplifier of the sweep generator during certain portions of the sweep voltage cycle. These oscillations are caused Whenever the potential of the plate of an electron tube is below cathode potential while the control or screen grid is above cathode potential, as favorable conditions arise for the electrons leaving the cathode and attracted by the positive grid but repelled by the plate to swing back and forth through the grid, therebyl generating radiant energy of appropriate frequencies which may cause serious interference in nearby circuits as well as in the electron tubes own circuits. It has been observed in television receivers that such oscillations produce a bar in the left hand side of the screen that is very objectionable. Shielding might reduce 'the amount of picture distortion but this means experimentation with each new model andv circuit arrangement whereas employment of the invention herein disclosed elieminates the trouble at its source.

This phenomenon, generally known as Barkhausen oscillations or positive grid oscillations, is especially troublesome in the type of transformer coupled stages that are generally used in sweep circuits for cathode ray tubes and especially in circuits employing magnetic deection, because of the rapid decay of the energy stored in the transformer and in the magnetic deilection coils.

The amplitude of the oscillations set up in the grid circuit in this manner is proportional to the number of electrons that pass back and forth through the grid structure at the same time, and the novelty of my invention lies in the fact that the electrons in each section of the stream are repelled so as to pass through the grid structure at different times. This. is accomplished by tilting the plate with respect to the other elements of the amplier so that repelling force exerted by the plate on the electrons moving toward it is different for different parts of the electron stream, and accordingly electrons in different parts of the electron stream reverse their direction of travel and start back toward the grid at different times. The building up of oscillations is thus prevented by rendering the swinging of the various electrons incoherent in time, or dissynchronous.

Accordingly, it is an object of this invention to provide a method and means whereby Barkhausen oscillations arev eliminated in amplifiers used in circuits that create a favorable environment for them.

' Itis a further object to provide a transformer coupled output circuit in which Barkhausen oscillations are eliminated.

It is a further object to provide amagnetic deflection circuit in which Barkhausen oscillations are reduced to a minimum.

These and other objects will be apparent from a detailed description of the drawings in which:

Figure l shows a transformer coupled circuit;

Figure 2 shows a tube having coaxial cylindrical elements embodying a form of the present invention;

Figure 3 shows a tube having a double truncated cone tapering to a smaller radius at the center;

Figure 4 shows a tube having plane electrodes;

Figure 5 illustrates a tube having an axial electrostatic field established by end plates.

In Figure l there is shown a circuit in which favorable conditions for the occurrence of Barkhausen-Kurtz oscillation exist, comprising a source 2 of voltage waveforms 4 which are applied to a control grid I of a tube 8. Tube 8 also has a cathode Il), which may be grounded, a screen grid I2, and a plate I4 which is-con nected to a source of B+ direct potential I6 via the primary I8 of a coupling transformer 25. The secondary 22 of the transformer is connected to a load 24, which may be the magnetic sweep coils for a cathode ray tube, and a damping diode 26 is connected in parallel with the load.

Consideration of the waveform 4 shows that at point A the rate of change of the current in the primary I8 goes from a highly negative value to a positive value, and according to Lenzs law, this change in an inductive circuit introduces an electromotive force of such polarity as to counteract the change. Accordingly, the plate I 4 is driven highly negative. In other words since the change at this point in the waveform is in a positive direction, the induced voltage acts to oppose an increase in current which means that the plate is driven in a negative direction. Because this electromotive force is introduced in primary I8, the plate may be driven negative with respect to both the screen and the cathode, and if this happens at a proper speed with respect to the transit time of the electrons in the tube, Barkhausen oscillations are set up which seriously interfere with the proper operation of the sweepcircuits.

In order to overcome this diiculty, a tube having a plate that is mounted dissvmmetricallv with respect to the cathode and grids is used in place of the normal type amplier Such a tube is illustrated in Figure 2 in which the cylindrical grids 30 are coaxial with the cathode 32. and the plate 3Q is in the form of a truncated cone that .is also coaxial with the cathode. It is apparent that such a structure varies the potential gradients in the vicinity of the plate and that accordingly the electrons passing from the cathode to the nearer part of the plate are repelled by the negative value of the latter occurring at point A of the waveform 4 before the electrons passing from the cathode to the opposite end of the plate. Therefore, the electrons pass back through the screen grid 30 at diierent times and therefore their eiects on the screen grid circuit are individual and not accumulative. Furthermore, arrow 38 indicates a component of electrostatic potential gradient parallel to the axis of the tube that serves to force the electrons in the opposite direction and remove them from the inuence of the plate before they can be drawn back through the screen or screens 30. This coaxial movement of the electrons is of course greatest when the velocity of the electrons is reversed by either the plate or the cathode.

This new combination of a tube having dissymmetrically located electrodes and a circuit that functions so as to drive the plate negative with respect to the screen grid of the tube operates to produce a new result, namely, the elimination of oscillations produced by velocity modulation of the electrons.

Although the invention has been explained in connection with a sweep circuit, it is apparent that the same new result is obtained in any circuit in which conditions are favorable for Barkhausen oscillations.

Another construction of a tube embodying the principles of the invention is shown in Figure 3 in which the potential gradient between the screen grid and the plate is progressively different along the axis of the tube, and in which the electrons that start to oscillate are swept axially in both directions along the tube and out of the control of the elements of the tube or electron discharge device. Numeral 40 indicates a plate structure that is in the form of similar truncated cones having their smaller ends joined and both of them being in coaxial alignment with respect to the cathode 42 and grids 44 and 46.

Figure 4 illustrates another construction in which plane electrodes are used, that is the elements of the tube lie in separate planes as distinguished from the elements in the devices previously discussed in which the elements are substantially in the form of concentric cylinders. Numeral 48 indicates the plate and the grids and cathode are indicated by numerals 50, 52 and 54 respectively.

Another construction for reducing Barkhausen oscillations is illustrated in Figure 5 that depends upon a substantially axial electrostatic field to remove the electrons from the control of the elements of the tube when they turn around to start their journey back through the grid structure. The plate 56 is shown to be in the form of a cylinder that is in substantial coaxial alignment with the cathode 58, and the grid structure 69. End plates 62 are mounted at either end of the tube elements and are insulated from them by insulator 64. Although they are shown to be in the form of annular rings, they may be of another shape such as a disc and still be capable of operating in accordance with the teaching of the invention. Now if one of these end plates is connected to a source of positive potential and the other to a source of lower potential, the electrostatic field between the cathode 58 and the plate 56 will have a component that is parallel to the cathode and electrons will be swept out of the space between the plate and cathode when they slow down and turn back to start the Barkhausen oscillations described above.

Normally, the tube elements described in connection with Figures 2-5 are enclosed in an evacuated envelope 10.

Although this principle is applicable to a triode or a tetrode, it finds its best adaptation in a pentode or beam power amplifier, for the amount of tilting of the plate necessary to the practice of this invention does not have an appreciable eiect on the characteristics of such tubes, and, for the same reason, remote cut-off characteristics are not present.

What is claimed is: Y

l. A cathode ray deflection signal amplier comprising in combination an electron discharge device having a cathode, an anode, and at least one grid electrode spaced between said cathode and anode, the plane of said anode being tilted with respect to the plane of said grid, and a signal output circuit'connected to said anode, said output circuit including electromagnetic means fOl Sweeping a beam of electrons in accordance with a signal applied to a grid.

2. In combination an amplifier having at least a plate, a cathode and a grid, an evacuated en- Velope surrounding said plate cathode and grid, means for maintaining said grid positive with respect to sa-id cathode, said plate being dissymmetrically shaped with respect to the grid so that the electrostatic eld between said grid and said plate is different at different portions of said grid, an electromagnetic cathode ray beam Ideiiection circuit coupled to said plate, and means for intermittently discontinuing conduction of the tube.

3. A cathode ray tube deection system comprising la tube having a cathode, control grid, screen grid and a plate, a coupling transformer having its primary winding connected to said plate, said plate being tilted with respect to said screen grid so that when said primary winding oscillates at its resonant frequency and drives the plate negative with respect to the cathode the electrons repelled by the plate pass back through different parts of the grid at different times.

WILLIAM HENRY CHERRY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,596,405 Dechend Aug. 17, 1926 1,894,599 Round J-an. 17, 1933 1,957,327 Elser May 1, 1934 2,048,224 Snow July 21, 1936 2,048,232 Snow July 21, 1936 2,141,413 Schlesinger Dec. 27, 1938 2,172,316 Bowie Sept. 5, 1939 2,219,590 Fra-cker Oct. 29, 1940 2,225,325 Van Overbeek Dec. 17,1940 2,239,678 Jobst Apr. 29, 1941 2,250,184 Miller July 22, 1941 2,309,672 Schade Feb. 2, 1943 2,317,824 Strutt et al Apr. 27, 1943 2,440,418 Tourshou Apr. 27, 1948 2,465,041 Schleimann-Jensen et al Mar. 22, 1949 2,553,735 Adler May 22, 1951 2,568,395 Herold Sept. 18, 1951 FOREIGN PATENTS Number Countr 262,808 y Date Great Britain Mar. 31, 1937 

